Ford flywheels and flexplates are apparently a very vexing topic for many
people working on engine or
transmission swaps like I was.
As I researched the details for myself, it became very apparent that it's a
confusing topic for many folks and that there are various sites out there that
attempt to explain it. Since I had to read a bunch of sites to decipher things,
I decided to start my own page to pull all this together in one place.

NOTE: This page is specific to the (now) older Windsor Ford V8 engines, and my
specific work was on 302/5.0L
engines. That same basics should work on the 351/5.8L engines, and the 289
engines as well, but, I have not confirmed that. The information on this page
does NOT apply to the later 4.6L, 5.4L, and other "modular" engines! Extrapolating this information to anything
else should be done
only after careful comparison of actual parts or other authoritative sources of
information. Using the wrong flywheel or flexplate on your engine can - quite
literally - destroy it due to excessive vibration due to the wrong balance
weight, so use common sense and lots
of care in selecting the flywheel to use. I am not responsible if you break your
engine, transmission, or anything else as a result of you using the information
on this page. This information is for educational purposes only, and has no
warranty or guarantee of being correct for your particular needs.

Overview

As far as I can tell, there are two basic ways that the flywheels and
flexplates differed - size (diameter and number of teeth) and the amount of
imbalance that they contain (Many/most Ford V8 engines are externally balanced
from the factory). The size matters because it determines the number of teeth on
the flywheel and has to match the starter location that is cast into your
transmission bellhousing. The amount of imbalance matters because the entire
rotating assembly is balanced together, and externally balanced engines put part
of the balance weight onto the harmonic balancer and onto the
flywheel/flexplate. If you put a flywheel/flexplate with the wrong imbalance on
your engine and run it, your main and rod bearings will take a serious pounding
due to the vibrations and will likely give out in just a few miles of driving.

From my research so far, it seems that manual transmission applications
(flywheels) and automatic transmission applications (flexplates) generally used
the same sized pieces, and they will both be the same size, at least as far as
the ring gear goes. For example, you can talk about a 164 tooth flywheel or
flexplate - there does not appear to be unique sizing for automatic vs. manual
setups. That's not to say that the automatic vs. manual transmission units were
the same in any given year and model of car, just that they happen to be
available with the same tooth count on the ring gear in various applications.

Details

The table below shows the nine different possibilities you have. It is
important to note that not all of these combinations were ever used by the
factory, so it is entirely possible you will need to get aftermarket parts to
make your combination work. In addition to the two different imbalances used by
the factory, there are also places that offer flywheels and
flexplates with zero imbalance (also referred to as "internally balanced" on
some sites) - these are used when building a custom motor.
I mention it because that stuff is out there - so be aware of it if you
are working on a custom high performance motor that you do not know the entire
history of. Also, the 148 tooth units are very rare and not even
mentioned on many pages/sites I came across in my research. Apparently, they
were only used in a few "small" vehicles like the V8 Mustang II installations. You may
not be able to find this size flywheel/flexplate in the 50oz or "none" imbalance
configurations, at least not easily. The others possibilities should all be
readily available from either OEM
or aftermarket sources. Reproduction flywheels for stock configurations are
readily available - flywheels are considered a "wear" item and they do need to
be replaced once in a while, so you can get them pretty easily it you look
around a bit for them.

Transmission Flywheel/Flexplate
Requirement

164 teeth

157 teeth

148 teeth

Engine imbalance

50oz

Possibility #1

Possibility #2

Possibility #3

28oz

Possibility #4

Possibility #5

Possibility #6

none

Possibility #7

Possibility #8

Possibility #9

To figure out what you need, start with your engine and find out what amount
of imbalance you need. Then, figure out what size unit you require to match up
with your transmission bellhousing. Now you know what flywheel or flexplate you
need. Write down exactly what you need, and make sure you get the right unit. Research each item
individually to make it easier on your brain, then when you get a clear answer
on both of them, write it down for later reference, and use that information to
select the right part for your needs.

Interesting Tidbits

Here are some Interesting and possibly useful tidbits of information I ran
into while researching this.

AOD transmissions used a 164 tooth flexplate.

Mustang T5 transmissions used a 157 tooth flywheel and a 10.5" or 10"
clutch disc.

Ford light-duty trucks often used a 164 tooth flexplate and an 11"
clutch disc, though some heavy-duty trucks used much larger clutches.

C4 transmissions could have used any of the three tooth count flexplates
depending on the bellhousing used. In original applications, it roughly
corresponded to the "size" of the vehicle the transmission came in.

C6 transmissions could have used either the 157 or 164 tooth flexplates,
depending on which case it had. As with the C4, the size of the flexplate
generally seemed to follow the size of the car it was used in.

Ford changed the imbalance on the 302 (otherwise known as the 5.0L)
engines in 1981. Some sources list this change as 1980 in a confusing way,
but all of the reliable data I found said 1981 was the first year of the new
50oz imbalance motors. Thus, if your motor was built before 1981, then it's
a 28oz imbalance motor. If it was build in 1981 or after, it's a 50oz
imbalance motor. If you are not sure, use
Google to find ways to check for sure what you have.

Ford did not change the imbalance on the 351W (otherwise known as
the 5.8L) engines - they stayed at a 28oz imbalance. This means that mixing
a late model flywheel or flexplate between a 5.0L and 5.8L engine is a bad
idea. The same goes for the harmonic balancers...

If you are looking at custom/aftermarket parts, they may specify
"internal" vs. "external" balance. Internal balance means there is zero
imbalance in the flywheel or flexplate, and these should only be used on a
custom motor that is internally balanced.

Visual comparisons of the 164 and 157 and 148 tooth units should be very
obvious as to which is which. If you have a known unit laying around, you
can use it to compare against an unknown unit to see what it is.

Once you know what to look for, you can easily tell the difference
between 28oz and 50oz imbalance pieces by looking at the back side. The 50oz
units will have a much larger weight on them. Comparing an unknown unit
against a known unit is easy, and various websites have good side-by-side
photos of the differences you can educate yourself. Use
Google to find some samples and educate
yourself if you want to be a good junkyard spotter.

Starters can interchange between 164 and 157 tooth flywheels in many
cases, but not all cases. Check the original application data for the
transmission you are using to verify. Remember that the starter is bolted to
the transmission bellhousing and not to the engine. For example, late model
Mustangs (1986-1993, for example) used the same starter for manual
transmission applications (157 tooth flywheel) and automatic transmission
applications (164 tooth flexplate).

You can change between the different balances, but it's expensive. You
can do this if you are willing to have your motor re-balanced (which
basically requires tearing it down like you would for a full rebuild) and
you are willing to replace various parts (like the flywheel and harmonic
balancer). It can be costly to re-balance the motor separately from a
rebuild, but it can be done in some (most?) cases if needed. I'm only
mentioning it because some folks are doing oddball/custom motor work or
fitting a swap into an "unusual" body that dictates size requirements, and
it's a possibility to keep in mind.

Pictures

157 tooth flywheel sitting on top of a 164 tooth flywheel - you can see the
164 tooth flywheel peeking out from behind the 157 tooth flywheel, showing the
size difference.

164 tooth flywheel (left) and 157 tooth flywheel (right) - you can see the
size difference if you look closely. You can also clearly see the clutch
operating area on the smaller flywheel on the right. A bigger clutch means more
holding power with less force, which is why you often see the larger 11"
clutches and 164 tooth flywheels used in the trucks and larger cars, and the
smaller 10" or 10.5" clutches and 157 tooth flywheels used in the smaller cars.

Rear of 164 tooth flywheel. Part # is E8TR-AA. This flywheel was removed from
a 1989 F150 with a 5.0L and a 5-spd manual transmission and uses an 11-inch
clutch. It is a 50-oz imbalance flywheel. Note the size of the imbalance weight
in the upper right area of the flywheel. Because this flywheel is larger in
diameter than the 157 tooth unit below, the weight has to be a bit smaller to
achieve the same balancing effect.

Rear of 157 tooth flywheel. Part # is E1ZR-6360-AA. The writing on it claims
it to be a late-model Mustang piece (unconfirmed as of yet), and it is a 50oz
imbalance flywheel. I believe this flywheel uses a 10" or 10.5" clutch. Note the
size of the imbalance weight in the upper right area of the flywheel. Because
this flywheel is smaller in diameter than the 164 tooth unit above, the weight
has to be a bit larger to achieve the same balancing effect.

NOTE: Previous versions of this page were in error on the captions for
the last two pictures. They incorrectly said the imbalance weight was in the
upper left area of the flywheels pictures - they are actually in the
upper right area. The text above has been corrected. Kudos to Dan Harris
(TigerDan) over at Ford Truck Enthusiasts
for spotting the error and letting me know about it so I could fix it. Apologies
to earlier readers who must have assumed I was lysdexic, or drove themselves
crazy trying to make sense of the mis-matched photos and text. Sorry. I would
like to point out that it took someone a year after I posted the page to point
the error out to me. Shame on
everyone else for not taking their chance to harass me about my mistake and get
immortalized here as a sharp-eyed and helpful reader the way Dan did! :-)
Thanks, Dan! Many future readers of this page have you to thank!

This is a 164 tooth flexplate from a 1993 5.0L with an AOD transmission. It
is a 50oz imbalance unit. In the first picture, you can see the large weight to
the upper left and the large "window" in the lower right. I believe this is the
side that faces the engine - you can see the clean area from the crank flange
with the minor grease staining around it. In the second picture, you can see the
window to the left and the discoloring from the welds for the weigh on the
right. I believe this is the side that faces the transmission - you can see the
clean spots from the bolt heads and washers at the crank flange mounting.

This is an example of a what I believe is 157 tooth flexplate that
would fit a 1979 F100 with a C4 transmission. It is a 28oz imbalance unit. The
weight is slightly smaller than in the previous unit, and there is no window on
the opposite side to make the weight have more of an effect. The picture is
taken from RockAuto.com as an example
since I didn't have any of these around to take pictures of. Their online parts
catalog with pictures is awesome, and so are their prices.

For reference, this is a comparison of a 28oz harmonic balancer
from a 1979 F100 with a 302/5.0L and a 50oz harmonic balancer from a 1985
Mustang with a 302/5.0L. The 28oz unit is on the left (more rusty/less greasy)
and the 50oz unit is on the right (more greasy/less rusty) in both photos.
Notice they both use the same 4-bolt pulley mounting. Notice the subtle
difference in the size of the imbalance weights and the location of the rubber
ring in relation to the inner hub by looking carefully at the top section of
each of them in the first photo. The 28oz imbalance unit has the rubber ring
further out from the center and has less metal removed from the outside of the
rubber ring at the top. The 50oz imbalance unit has the rubber ring closer to
the center and more metal removed from the outside of the rubber ring at the
top. This difference in imbalance due to the different amounts of "missing
metal" from the outer ring is what makes them different imbalances.

Comments? Kudos? Got some parts you'd like to
buy/sell/barter/swap? Nasty comments about my web page so far? You can email
Mike or
Debbie.